The invention relates to a cable assembly having a strain relief mechanism and a combination of such a cable assembly in a housing
Many electrical systems require cables to be attached to electronic or electrical components within a casing or housing containing the components and then emerge from an opening in the housing. Such cables can carry, for example, electrical signals from electrical circuits in one housing to circuits in another housing. Such cables are often subject to lateral and longitudinal stresses and strains which, if they are severe, may pull the cable out of the housing and detach it from the electrical or electronic component, leading to failure of the system.
A number of prior art constructions have been developed in order to protect the systems. For example, U.S. Pat. No. 4,900,266 (Sainsbury et al), assigned to GSI Corporation, teaches a cable and connector assembly in which a pair of strain-bearing cables are embedded in and extended longitudinally along the side edges of a ribbon cable. A circuit board member is formed with two passages which serve to receive a free end of the strain-bearing cables. The free ends of the strain-bearing cables are threaded through the passages and are bonded by means of an adhesive or the like to the circuit board member. The free ends may also be tied in a knot after being threaded through the passages so that the free ends are held fast with respect to the circuit board member. The assembly of this disclosure thus requires additional passages to be constructed in the circuit board member to accept the free ends of the strain-bearing cables. The circuit board member of this disclosure fulfills two roles. It serves to accept the conductors from the cable at connection points, and furthermore it acts as an anchoring element for the strain-bearing cables.
In a similar approach it is known in the art to attach strain-bearing cables to a circuit board member by means of a screw or post attached to the circuit board, around which are tied the ends of the strain-bearing cables.
Another approach to strain relief mechanisms is taught in U.S. Pat. No. 5,414,218 (Nathan) assigned to Alfred Karcher, GmbH and Co., in which a recess is formed between a double walled housing. A cable tensile strain reliever consists of a sheath and a clamping part. The clamping part is placed on the cable and thus constricts the cable, pressing the individual wires within the cable against the insulation of the cable. The sheath is provided with two annular grooves which are so designed that they fit into recesses in the two walls of the double walled housing such that a mechanically stable connection is ensured between the housing and the cable tensile strain reliever. Since the clamping part is constricted against the insulation of the cable, the external tensile forces can no longer be transferred to the connection points in the interior of the apparatus via the individual wires, but are transferred via the insulation of the cable to the clamping part and from there via the sheath to the housing. The cable tensile strain reliever of this disclosure thus requires both the design of the housing and the design of the sheath to be optimised with each other to ensure maximum protection.
The same Nathan ""218 patent teaches a second embodiment in which a cable tensile strain reliever can be used with a single-walled housing. In this embodiment, the sheath is provided with a flange-like extension which is disposed within the housing. In this position, the extension transfers to the housing tensile forces which are exerted on the cable tensile strain reliever and directed towards the interior of the housing.
In the embodiments of the Nathan ""218 patent, the sheath is made of an elastic plastic material such a polyvinyl chloride, polyurethane or a mixture of these two substances, or of a rubber material which is vulcanized onto the cable.
U.S. Pat. No. 4,857,674 (Filbert), assigned to Leviton Manufacturing Company, discloses a strain relief mechanism similar to the second embodiment of the Nathan ""281 patent, in which a strain relief device made of a flexible material such as hard rubber carries a cable 14 running through a conduit in its body. The strain relief devices has two flanges mounted on one end which can be inserted through a hole in a casing or housing. The strain relief device is locked in place through rotation.
Clamps as strain relief mechanisms are also known in the art. U.S. Pat. No. 5,742,982 (Dodd et al.) teaches one such clamp assembly for one or more cables which is made in two clamp halves connected together by a hinge pin. One clamp half includes a pair of countersunk apertures to attach the clamp half to a fixed structure from which the cable or cables will be supported. The cables to be strain relieved enter into cavities within the clamp assembly and two clamp halves closed on each other. A nut tightens the clamp onto the cables therein to hold the cables tightly within the clamp assembly.
Another type of clamp is known from U.S. Pat. No. 4,758,179 (Klein et al), assigned to the Zippertubing Company, in which the housing has a sub-assembly through which an electrical cable passes before entering the housing. The sub-assembly has a pair of identical elongated metallic clamping members formed along their adjacent sides and which have sharp edge projections. On closure of the sub-assembly, the clamping members are tightened, causing the sharp edged projections of these members to bite into and form a strong anchorage with the jacket.
U.S. Pat. No. 5,980,298 (Johnson), assigned to National Instruments Corporation, teaches a further form of a strain-relief device which comprises a clamping portion including a fastener. The clamping portion has a slot through which a cable, such as a ribbon cable, can be passed and clamped in position. The fastener is used to releasably attach the clamping device to an electrical device housing.
Another older type of claim is known from U.S. Pat. No. 3,258,234 (Fernberg) assigned to United-Carr Inc. in which a cable passes through a fastener comprising a stud and an insert. The cable is inserted into the stud and then into an aperture of a support panel. The insert is brought up to the stud and pressed firmly home onto the stud so as to trap the cable securely in the stud. In the final position the cable is held securely in the support panel by virtue of the right-angled bend in the cable and the grip obtained on the cable between the insert and the shank of the stud. Any strain or pull on the cable on the other side of the panel is transmitted only to a substantially reduced extent.
From U.S. Pat. No. 5,975,924 (Daoud), assigned to Lucent Technologies, a strain relief mechanism is known which uses a conductive sleeve inserted into one end of a multi-line phone cable. The conductive sleeve has a threaded stud attached which is used to secure the conductive sleeve and hence also the phone cable into a conductive bracket.
An object of the invention is to improve the strain-relief mechanisms of cable assemblies.
A further object of the invention is to simplify the manufacture of cable assemblies incorporating strain relief mechanisms.
Yet a further object of the invention is to reduce the manufacturing time for electronic devices using cable assemblies with strain relief mechanisms.
These and other objects of the invention are solved by providing a cable assembly with a cable having a plurality of conductors and a strength member with member ends disposed in the cable assembly. At least one independent anchoring element is attached to at least one of the ends of the strength member and has an opening provided therein. The member end of the strength member passes through the opening of the anchoring element. The independent anchoring element is separate from the printed circuit board to which the plurality of conductors are connected and also from the housing or casing in which the printed circuit board is disposed. Thus neither the housing nor the printed circuit board have to be specially designed with anchoring points to accept the strength member. Furthermore, large stresses placed on the cable and hence on the anchoring member will not lead to potential destruction of a costly printed circuit board.
In a preferred embodiment of the cable assembly the opening is in the form of an eyehole disposed within the anchoring element. In this embodiment, the strength element cannot slip out of the opening, since it is enclosed on all sides by the anchoring element. A particularly advantageous embodiment of the invention uses a cable shoe with an eyehole disposed therein. This is a standard part which is available freely and is consequently cheap.
The cable assembly can also be provided with a cable sleeve attached to at the least one end of the cable. This cable sleeve provides stability and rigidity to the ends of the cable and thus allows the lateral and longitudinal stresses to be transmitted to the casing or housing into which the conductors of the cable assembly enter.
The cable sleeve is most advantageously provided with a fixing lip into which the walls of the casing can slot, and the cable assembly is thus held in position. The eye of the cable shoe is disposed at the end of the cable sleeve and thus, when logitudinal forces are exterted on the strength member, the cable shoe is pulled against the end of the cable sleeve.
The object of the invention is also solved by providing a combination of a casing and a cable assembly attached to the casing. The cable assembly has a cable with a plurality of conductors and a strength member with member ends disposed within the cable assembly. At least one anchoring element is attached to one of the ends of the strength member. The anchoring element is disposed within the casing and has an opening through which the strength member passes. Thus, when longitudinal or lateral stress or strain is applied to the cable assembly, the anchoring element is pulled against the wall of the casing to which the stresses are transferred.